1. Field of the Invention
The present invention relates to a thermal printer free from the falling-off of a platen even if a printer cover is irregularly operated, and a portable type terminal equipment to which the thermal printer is connected.
2. Description of the Related Art
In the conventional thermal printer, when a printing medium such as a paper sheet is set in the thermal printer, a printer cover is initially opened, and the end of the printing medium, wound usually in the form of a roll, is then inserted into a gap between a printer head and a platen which is in contact with the printer head and rotates to feed the printing medium during the printing operation. Thereafter, the printing medium is pushed into an accommodation space therefor and, finally, the printer cover is closed to complete the setting operation. However, as the gap between the printer head and the platen is as small as several millimeters and, therefore, care must be taken when manually passing the printing medium through the gap, a considerable time is required and an excessive load is placed on the user.
To solve this problem, a thermal printer is known in that the platen is not fixedly arranged with respect to the printer head but provided in the printer cover so that the platen is brought into contact with the printer head when the printer cover is closed (for example, Japanese Patent Publication No. 3096702 (page 2, third paragraph and attached drawings)). In this structure, the user pulls an end of the rolled printing medium, several centimeters long, to the outside after opening the printer cover upward and, then, puts the printing medium into the accommodation space therefor, and then the printer cover is closed. Thus, the printing medium is set in the printable state by simple steps. Generally, this type of thermal printer is called as an easy-loading printer.
FIG. 4 of the attached drawings illustrates a side sectional view of the conventional thermal printer coupled to one end of a portable type terminal equipment widely used for meter inspection or inventory management in the distribution field. A printer cover 30 comprises an upper cover 18 and a lower cover 19, and the upper cover 18 is connected to the lower cover 19 by a hinge 22 and is opened and closed about the pivot axis of the hinge in the direction shown by the arrow c. A platen 20 is provided in the upper cover 18 in a semi-fixed state so that when the upper cover 18 is opened upward, the platen 20 also moves upward together with the upper cover 18. This thermal printer is adapted to be detachable from the portable type terminal equipment by the application of a certain force at the end of the printer cover 30 in the direction of the arrow A, by the user, which may preferably accompany the movement in the clockwise direction (as shown in FIG. 4 by the arrow a), when the printer is not necessary. However, if a force is applied in the counterclockwise direction b to the printer cover 30 by mistake, or from outside by accident, the printer cover 30 can be detached from the portable type terminal equipment, but as apparent from FIG. 4, the printer head 24 is inclined slightly rightward and brought into contact with the platen 20 and there is a problem in that the platen 20 remains while being in contact with the printer head 24 due to the pressure of the printer head 24 if the force is applied to the printer cover 30 in the counterclockwise direction b. This may cause a failure of the platen 20 or other peripheral parts.